This invention relates to a weigh scale apparatus and more particularly to a scale which employs a beam type flexure element and means to detect bending of the beam as a measure of the applied load.
Weigh scale apparatus, other than the laboratory balanced type, typically comprise a spring element such as a coil or wrap spring or a torsion bar which is deflected in proportion to applied loads. The traditional means for sensing spring deflection are such that it is difficult and expensive to attain a high degree of accuracy. Thus, an inexpensive device is typically not precise is its measurements. Moreover, the prior art scales are also typically quite sensitive to the point on the pan or load receiving surface at which the load is applied; i.e., a non-centered load on the pan tends to produce an inaccurate reading.
In U.S. Pat. No. 3,938,603, assigned to the assignee of the present application, a constant moment weigh scale is disclosed which overcomes noted disadvantages of the prior art by providing a scale which can be manufactured so as to produce an extremely high degree of accuracy with relatively little expense and which is relatively insensitive to non-centered load application. The scale of U.S. Pat. No. 3,938,603 includes a base; a load receiving member such as a pan; a pair of pivot members spaced apart and disposed mechanically between the pan and the base so as to experience a turning moment when a load is applied to the pan; and a beam connected to a hence "floating" between the two pivot members. The turning moments of the pivot members generated in response to application of a load to a pan are applied to opposite ends of the beam to cause a bending deflection of the beam and means are provided at the center of the beam for measuring the tension and compression forces in the beam due to the bending. The apparatus is constructed such that the bending movement at the center of the beam is a constant value regardless of the position of a given weight on the load receiving member. This scale, while generally satisfactory in most typical applications, sometimes can pick up "cross-talk" or spurious input signals in the beam resulting from excess or cumulative manufacturing tolerances in the various parts or resulting from disposition of the base of the scale on an imperfect support surface.
The present invention retains all of the noted advantages of the scale of U.S. Pat. No. 3,938,603 while providing a simple and effective means for compensating for spurious input signals resulting from excess tolerance variations, misalignment, or deflections of the base structure.